1. Field of the Invention
The present invention relates to a Mannich reaction product and a process for producing the same and the use of the product, and particularly relates to a Mannich reaction product useful as a detergent-dispersant for lubricants, a process for producing the same, a detergent-dispersant containing said product, and a lubricating oil composition containing said detergent-dispersant. 2. Description of the Related Arts
Generally, conventional ash-free type detergent-dispersants including succinimide-based ones and hydroxybenzylamine-based ones, have been used extensively as additives for gasoline, diesel-engine oils, being valued highly for their remarkable actions of dispersing fine particles. These are regarded as very important additives for lubricants, because they have synergistic effects with dialkyl zinc dithiophosphate or metal-type detergent-dispersants. Recently, however, their insufficient stability at high temperature have often been pointed out.
Japanese Patent Publication No. 43631/1971 discloses, as an ash-free type detergent-dispersant stable against oxidation having an improved oil-solubility, a reaction product obtained by reacting the reaction intermediate of alkylphenol, formaldehyde, and polyalkylene polyamine with alkenyl succinic arthydride, or a reaction product obtained by reacting the thus resulting product with a boron-containing compound. Japanese Patent Application Laid-Open No. 8304/1976 discloses a reaction product obtained by reacting the reaction intermediate of alkenyl (snhydrous) succinic acid and polyalkylene polyamine, in the presence of aidehyde, with an aromatic alcohol (for example, alkylphenol, phenol, and thiodiphenol). Also these reaction products, however, are insufficient in stability at high temperature.
Further, Japanese Patent Application Laid-Open No. 168492/1988 discloses a reaction product obtained by reaction with a glycolic acid in place of the boron-containing compound described in Japanese Patent Publication No. 43631/1971, but it is insufficient in stability at high temperature, also.
Conventional lubricating oils for internal-combustion engine comprise a base oil, an ash-free type detergent-dispersant such as polybutenyl succinimide, and metal-type detergent-dispersant such as sulfonate and phenates of alkaline earth metals, and anti-wear agents such as alkyl zinc dithiophosphate. The metal contents in the components of additives are combined with oxides and sulfates by combustion, which might be responsible for environmental pollution.
In recent years, among the internal-combustion engines, particularly in diesel engines, measures to counter the environmental pollution by inhibiting particulates and NOx in exhaust gas have become important subject. To counter the environmental pollution, exhaust gas purifiers such as particulate traps and exhaust gas removing catalysts are used, but these means do not prevent blockage of the system by metal oxides or sulfides resulted from combustion by the use of conventional lubricating oils for internal combustion engine. In this regard, there rose the need for a lubricating oil for internal combustion engine which can reduce the blocking by these metal oxides or sulfides to as little as possible.
In order to meet this need, Japanese Patent Application Laid-Open No. 163294/1989 discloses an ash-free type lubricating oil composition for internal combustion engine including diesel engines, comprising a conventional ash-free type detergent-dispersant, sulfurized alkylphenol and a metal deactivator. Although the composition has the feature of being ash-free, it has insufficient stability at high temperatures.
The present inventors have made researches to dissolve the defects in the prior arts as described above, and develop a substance useful as a detergent-dispersant being excellent in stability at high temperature and having a stability against oxidation.
The present inventors found that a reaction product having excellent stability at high temperatures by using a specific sulfurized alkylphenol in place of the aromatic alcohol described in Japanese Patent Publication No. 43631/1971 and Japanese Patent Application Laid-Open No. 8304/1976. The present invention has been accomplished basing on this finding.